I think there should be more things that can hurt the player if done wrong: poisonous fish, drinking saltwater, some uncooked food items, getting caught in bad weather, running the fatigue meter down, touching jellyfish in the item nets with bare hands, touching spikes. Things that would be common sense or can be learned through trial and error. The only way to get hurt right now is by the shark, which you never have to worry about if you never leave the raft. There would be more challenge and variety to the dangers the player faces. I think it'd be good since players can eat food to restore health, and in later gameplay it's all too easy to keep the hunger bar full.

^ Working with dangerous items like spikes, traps, fire, or stronger fish on a hook could require skill checks that hurt the player if failed.

More reasons to get in the water. Perhaps bigger nets or underwater structures that require getting wet to place and repair. I feel like just making the sharks more numerous or more destructive would get more frustrating than fun, and it'd be more interesting if part of the challenge was from players themselves risking the shark.

^ To discuss an already-existing reward: I recently found out that if I regularly combat the shark(letting it bite me and so I can hit it until it dives under) my raft is attacked way less. Please please keep this in. I find it allows me to work on my raft on my own time without getting interrupted, plus I'm eating food as soon as I can produce it to keep my health up, so I don't have a crazy surplus of potatoes. Also it's fun decorating the seas with the carcasses of my enemies >:D I always have something to keep me engaged by playing this way.

Shark repellent that works on a time limit, maybe something crafted from poisonous fish/plants that affects so much area for a few minutes. This could help a player defend larger rafts or let them sleep securely if that's implemented.

Fires should require fuel. In order to use the water purifier or cooking station __ number of times, they could be stocked with planks or thatch or rope in various amounts.

A standard, multi-use campfire. Food or water can be cooked with equipment add-ons, and items that require heat to make can be crafted there.

The ability to dive down a few feet. The player could use it to dodge the shark or even pursue it when it dives itself. Maybe shallow sealife could be encountered. But even if there's nothing to see under the water it would keep the player from getting stuck under the raft(about which I already submitted to the bug forum).

Have scrap exclusively come in barrels while removing palm seeds. Have coconuts float by as a rare item. Allow rope to be an uncommon barrel-item. As the game is right now I think this would cause some balance problems, but if it could be done later I think it would feel more realistic.

These ideas are more "out there" but would be pretty cool:

A free-diving game mode. Not so much open-world but limited movement and visibility. Presuming that the raft and player are drifting on the ocean currents, they wait for their playable area to move over new items stuck to the ocean floor. It would be very similar to how resources float by the raft on the surface, except the player grabs everything by hand.

^This would only be possible during special events, when the raft is drifting over a shallow area. The player has the opportunity to dive once per event.

^ The player would need to craft a tether and post so that they 'anchor' themselves to the raft. It'll explain why they can't go far.

^There's a breath meter. Running the meter down starts decreasing health until the player surfaces or dies. Not sure about the fatigue meter. The player can risk running out of breath by waiting to drift over good items.

^The player could collect things like sand, rocks, decorative shells, and seaweed, and could grab crabs or spear fish.

Hard Mode: Rats. An extra challenge in addition to the shark. They float in on barrels, hide in palm trees, can climb pillars and walls, can chew through chests and destroy items inside, gnaw on potatoes, bite the player if held too long, and eventually multiply if two can make a nest. The player can get rid of the rats by eating them or throwing them off the raft(hope that they're whisked away by the current before they swim back). They can't chew through chests, walls, doors, or floors that are reinforced with metal.